In an LTE (long term evolution) system, received-signal orthogonality depends on a scenario in which a transmitter and a receiver work on completely the same frequency reference points. If frequency reference points are not completely the same, subcarrier orthogonality is damaged, and a subcarrier leakage is caused. To avoid the subcarrier leakage, a base station needs to perform frequency offset estimation on a terminal device, and calibrate a frequency of the terminal device by using an estimated frequency offset value.
A TTI (transmission time interval) in a current LTE system is 1 millisecond. In an uplink in the current LTE system, on a PUSCH (physical uplink shared channel), DM-RSs (Demodulation RS, demodulation reference signal) are sent on two SC-FDMA (single carrier frequency division multiple access) symbols at each 1-ms TTI, so that a base station measures and estimates an uplink channel. In addition, the base station performs, according to a phase difference between the two DM-RS symbols, frequency offset estimation and frequency calibration on a PUSCH sent by a terminal device.
To achieve a shorter round trip time and a shorter data transmission delay. an evolution scheme of the current LTE system has proposed a scenario in which a TTI length is set to 0.5 millisecond or to be shorter than 0.5 millisecond. Correspondingly, after the TI length in the LTE system changes from 1 millisecond to 0.5 millisecond, according to a prior-art signal structure, a DM-RS used to estimate an uplink frequency is sent on only one symbol. Consequently, the base station cannot perform accurate uplink frequency offset estimation and calibration on the terminal device by using the DM-RS on the symbol.
To resolve a problem occurring when uplink information is demodulated at a 0.5-millisecond TTI, a most intuitive solution is to add a DM-RS symbol to the 0.5-millisecond TTI. In this way, the base station can perform accurate uplink frequency offset estimation by using DM-RSs on two SC-FDMA symbols.
However, because the DM-RS symbol is added to the 0.5-millisecond TTI, such additional reference signal overhead results in a smaller capacity of data that can be transmitted at the 0.5-millisecond TTI. In this manner, data transmission efficiency is reduced, and reference signal system overheads are increased.